Sodium-ion stimulated amino acid uptake in membrane vesicles of alkalophilic Bacillus no. 8-1

Abstract

Membrane vesicles were isolated from alkalophilic Bacillus No. 8-1, and the active transport of amino acids was studied. The transport of amino acids was dependent upon substrate oxidation and the presence of Na+. Concentrative uptake of amino acids was stimulated by the addition of an artificial electron donor system, ascorbate-phenazine methosulfate (PMS), and to a lesser extent by NADH, while succinate, L-lactate, and alpha-glycerol-phosphate did not stimulate the uptake. N,N,N',N'-Tetramethyl-p-phenylenediamine (TMPD) and cytochrome c were able to replace PMS, and reduced forms of these compounds were also very efficient electron donors. Amino acid transport was dependent on electron transfer, and inhibition of NADH oxidation by cyanide, 2-heptyl-4-hydroxyquinoline-N-oxide (HOQNO), and sodium azide directly prohibited serine transport. The pH optima for serine transport lay between pH 8 and 9 for all energy sources. Sodium ion stimulated serine transport in the presence of NADH, NADH plus cytochrome c or succinate plus PMS, but had no stimulatory effect on the corresponding dehydrogenase activities. Sodium ion was also required for accumulation of serine in response to an artificial membrane potential where the respiratory chain was not operative. These results indicated that the stimulatory effect of Na+ on amino acid uptake was on the transport process itself.